LABORATORY  MANUAL 

FOR 

SOIL  PHYSICS. 


By  J.  G.  MOSIER 


/   BERKELEY   \ 


EAfiTH  n 

SCIENCES  A      ,  4.     n  ..         „ 

-<k>^.  ay.  /9/o 


EAflTH 
CIENCE 
LIBRARY 


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SCIENCES 
LIBRARY 


PREFACE. 

The  laboratory  practices  described  in  this  manual  are  designed  for 
one  semester's  work,  during  which  it  is  hoped  to  give  the  student  a 
knowledge  of  principles  that  underlie  many  common  agricultural  oper- 
ations. No  very  complicated  apparatus  is  required,  but  great  care 
must  be  used  to  have  uniform  conditions,  especially  where  different 
soils  are  to  be  compared. 

In  this  second  edition  many  changes  have  been  made  that  the 
experience  of  the  past  three  years  seemed  to  indicate  as  best.  Some 
new  Practices  have  been  added,  together  with  cuts,  descriptions  of 
apparatus  and  forms  for  the  data  obtained. 

In  a  number  of  practices  students  may  work  together  in  groups 
not  so  large,  however,  but  that  each  one  may  have  a  distinct  problem 
to  work  out  in  each  practice.  This  will  enable  the  class  to  complete 
the  work  in  one  semester  which  otherwise  might  not  be  possible. 

ACKNOWLEDGEMENTS. 

These  laboratory  practices  were  not  all  originated  in  the  Univer- 
sity of  Illinois.  Nos.  9, 11,  14,  18,  20,  21,  and  22  have  been  adapted  to 
our  work  from  Ohio  State  University  Bulletin  No.  6  by  Professor 
William  D.  Gibbs,  formerly  of  that  institution,  and  Practice  23  was 
taken  from  the  Manual  of  Soil  Physics  of  Purdue  University.  A  few 
of  the  practices  in  this  manual  had  been  arranged  for  student  use  by 
the  late  Mr.  H.  E.  Ward,  formerly  instructor  in  Soil  Physics  in  the 
University  of  Illinois. 

I  also  wish  to  acknowledge  the  valuable  suggestions  received  from 
Professor  Clifford  Willis,  now  of  South  Dakota  Agricultural  College, 
and  Mr.  A.  F.  Gustafson  of  this  University. 

The  Author. 
College  of  Agriculture, 

University  of  Illinois, 
Urbana,  Illinois,  June,  1908. 


LIST  OF  APPARATUS  FOR  EACH  STUDENT. 


1 

Ring  stand 

1 

Yard  cheese  cloth 

3 

Rings  (3  sizes) 

6 

Pint  jars 

1 

Bunsen  burner  with  rubber 

1 

Pair  crucible  tongs 

tubing 

1 

Desiccator 

1 

100  cc.  graduate 

L2 

Soil  pans 

1 

Wash  bottle,  500  cc. 

12 

Crucibles,  25  cc. 

1 

Nest  of  beakers  Nos. 

6 

Crucibles,  50  cc. 

2 

Funnels,  4  inch 

1 

Spatula 

1 

Trinagle,  pipestem 

1 

Camel's  hair  brush 

2 

Test  tubes 

1 

Towel 

1 

Box  matches 

STOCK  SOILS. 

1  to 


The  soils  commonly  used  consist  of  a  (1)  sand,  (2)  loam,  (3)  silt,  (4) 
clay,  and  (5)  peat. 

The  sand  is  a  white  quartz  of  medium  fineness.  This  is  en- 
tirely free  from  organic  matter  and  of  course  represents  an  extreme. 
A  sand  soil  as  taken  from  the  field  is  occasionally  used  for  purpose  of 
comparison. 

The  loam  is  a  mixture  of  sand  (not  over  50  percent)  silt,  clay  and 
organic  matter.    This  represents  a  good  type. 

The  silt  soil  is  one  in  which  silt  of  different  grades  forms  70  per 
cent  or  more  of  the  constituents.  It  is  a  very  common  type  of  soil, 
especially  in  glacial  or  loessial  soil  areas.  The  timber  phase  of  this 
type  is  used  in  the  laboratory  because  it  contains  less  organic  matter 
than  the  prairie  phase. 

The  clay  soil  used  is  a  heavy,  plastic,  sticky,  clayey  soil,  frequently 
found  in  bottom  lands  along  large  streams.  The  samples  used  should 
contain  30  percent  or  more  of  clay. 

The  peat  soil  is  obtained  from  peaty  swamps  or  bogs,  which  are 
especially  common  in  north  central  United  States.  Organic  matter 
usually  constitutes  about  75  percent  of  this  soil.  (Where  decomposi- 
tion has  gone  on  far  enough  and  much  clay  is  mixed  with  the  organic 
matter,  muck  soil  is  found.) 

The  soils  are  prepared  by  being  dried  and  pulverized  until  they 
pass  through  a  2  millimeter  sieve. 


M593629 


PRACTICE    1 
Determination  of  Capillary  Moisture*  in  Soils. 

Use  soils  collected  according  to  method  given  belowf  and  make 
the  determinations  in  duplicate  for  surface,  subsurface  and  subsoil. 
Weigh  carefully  six  soil  pans.  Place  in  each  from  100  to  200 
grams  of  the  soil  and  weigh  pan  and  soil  quickly  to  prevent  loss  of 
moisture.  Let  it  dry  at  room  temperature  for  72  hours,  after  which 
weigh  at  intervals  of  about  24  hours  till  a  practically  constant  weight 
is  obtained.  The  loss  of  weight  is  the  capillary  moisture.  Express 
your  results  in  grams,  and  after  the  completion  of  the  next  exercise 
express  the  results  in  percent  of  the  water-free  soil.  Use  these  air-dry 
soils  for  Practice  2. 

Express  in  tabular  form  the  capillary  moisture  in  grams  and  per- 
cent of  water-free  soil. 


*The  moisture  content  will  always  be  expressed  as  percent  of  the  water-free  soil 
in  these  exercises  unless  otherwise  stated. 

tFor  this  practice  and  also  for  Practice  5  the  students  are  required  to  collect  their 
own  samples.  For  this  purpose  a  one  and  one-half  inch  or  a  two-inch  auger  with  an 
extension  making  it  40  inches  long  is  used.  In  collecting  samples  for  moisture  determin- 
ations, expose  the  soil  as  little  as  possible  to  the  air  before  putting  in  jars.  Collect  the 
surface  soil  to  the  depth  of  the  plow  line,  usually  about  7  inches.  After  this  part  of  the 
sample  is  removed,  the  hole  is  enlarged  sufficiently  so  that  the  subsurface  soil  may  be 
taken  without  coming  in  contact  with  the  surface  soil.  Take  the  subsurface  sample  to 
the  subsoil  line  as  indicated  by  the  change  in  color,  texture  and  physical  composition. 
Commonly  this  line  is  found  at  a  depth  of  16  to20  inches,  Enlarge  and  clean  out  the  hole  as 
before.  Since  the  change  from  subsurface  to  subsoil  is  not  a  sharp  line  but  usually 
somewhat  gradual,  we  discard  about  two  inches  of  the  intermediate  mixture.  The  sub- 
soil is  then  collected  to  a  depth  of  40  inches,  if  possible. 

In  some  soils  the  subsurface  layer  may  be  absent,  the  subsoil  being  reached  by 
the  plow,  while  in  others,  as  in  peaty  and  sandy  soils,  no  true  subsoil  may  be  found 
within  40  inches  of  the  surface.    In  such  cases  only  two  samples  are  taken. 


PRACTICE  1 


Stratum 

Surface 

Subsurface 

Subsoil 

Sample 

1 

2 

1 

2 

1 

2 

Capillary  moisture   in  %  of 

PEACTICE    2 
Determination  of  Hygroscopic  Moisture. 

Use  air-dried  soils  from  Practice  1.  Mark  and  weigh  the  neces- 
sary number  of  crucibles  to  run  duplicates  of  each  stratum.  Place 
about  10  grams  of  air-dried  soil  in  each  crucible  and  weigh.  It  is  best 
to  weigh  all  of  the  duplicate  samples  out  at  the  same  time  so  as  to 
get  them  under  the  same  conditions  as  to  moisture.  The  hygroscopic 
moisture  of  a  soil  varies  with  the  relative  humidity  and  temperature 
of  the  atmosphere.  Heat  in  an  oven  at  about  100°  C.  for  at  least  five 
hours.  Cool  in  a  desiccator  and  weigh  rapidly  to  prevent  absorption 
of  moisture  from  the  air.  The  loss  of  weight  is  the  hygroscopic  mois- 
ture. 

Express  in  tabular  form  the  loss  in  grams  and  in  percent  of  the 
water-free  soil.  Also  the  total  moisture  of  the  samples  in  percent  of 
water-free  soil. 


PRACTICE  2 


Stratum 

Surface 

Subsurface 

Subsoil 

Sample 

1 

2 

1 

2 

1 

2 

Weight  of  crucible+air-dry  soil 

Weight  of  crucible  +  water-free 
soil 

Hygroscopic  moisture  in  Jo  of 

Av.    per    cent,    of    hygroscopic 

Av.  per  cent,  of  capillary  water 

8 
PRACTICE  3 

Effects  of  Drainage  on  Temperature  of  a  Soil.* 

Two  wooden  trays  3  by  4  feet  and  six  inches  deep,  one  lined  with 
zinc  to  prevent  the  loss  of  water  and  the  other  made  so  as  to  allow 
drainage,  are  filled  with  the  same  kind  of  soil.  Water  is  added  to  each 
till  drainage  begins  in  the  latter.  After  three  or  four  days  the  tem- 
perature of  each  at  1,  2,  and  4  inches  in  depth  is  determined  hourly 
on  a  clear  day. 

Explain  differences  in  temperature. 

Why  is  clay  land  liable  to  be  cold? 


"This  and  the  following  Practice  logically  come  later  in  the  course,  but  the  season 
here  makes  it  necessary  to  give  it  early  in  either  semester.  Better  results  may  be  ob- 
tained by  conducting  these  experiments  before  the  weather  gets  too  cold  in  the  fall  or  too 
hot  in  the  spring. 


PRACTICE  3 


Time 

Ther. 
1  inch  deep 

Ther. 
2  inches  deep 

Ther. 
4  inches  deep 

Drain'd 

Un- 
drained 

Drain'd 

Un- 
drained 

Drain'd 

Un- 
drained 

9         li 

10         " 

11 

12        " 

1        " 

2        " 

3        " 

4        " 

1 

10 

PRACTICE  4 

Effects  of  Color  of  Soil  on  Temperature. 

Fill  large  wooden  tray  6  feet  long,  3  feet  wide  and  6  inches  deep  with 
very  light  colored  soil,  gray  silt  loam,  well  pulverized.  Divide  the  tray 
lengthwise  into  halves  and  divide  each  half  into  six  plots  and  plant 
the  same  kind  of  seed  in  the  opposite  plots  putting  the  same  number 
in  each  but  covering  those  in  one  half  of  the  tray  I  inch  and  the 
other,  $  inch  deep.  Then  cover  the  latter  with  I  inch  of  black 
soil  so  that  all  of  the  light  colored  soil  is  covered.  Observe  the  num- 
ber of  plants  up  each  morning  and  evening,  keeping  a  careful  record 
of  the  number  coming  up  each  day. 

Select  a  clear  day  and  make  observations  on  the  temperature  of 
each  half  of  the  tray.  Insert  thermometers  1,  2,  and  4  inches  in  depth, 
also  place  one,  one  inch  above  surface  of  each  kind  of  soil,  and  take 
hourly  readings  from  8  a.  m.  to  5  p.  m.  Keep  all  parts  of  tray 
equally  moist. 

Each  student  may  look  after  the  planting  of  a  single  plot  but  he 
must  make  observations  on  all  plots  in  the  tray  and  keep  results  in 
tabular  form. 

Which  tray  shows  the  higher  temperature?    Why? 

Why  can  you  see  the  corn  rows  on  the  low  black  land  sooner  after 
planting  than  upon  the  higher  lighter  colored  soil? 


11 

PRACTICED 


Location 

of 

Ther. 

Time 

5 

8 

9 

10 

11 

12 

1        2 

3 

! 

1  inch 
above 

1 

Dark 

1  inch 
below 

Soil 

2  inches 
below 

1  inches 
below 

1  inch 
above 

Light 
Soil 

1  inch 
below 

2  inches 
below 

4  inches 
below 

|.... 

Number  of  plants  up  after  number  days  indicated  below: 

Light  Soil 

Dark  Soil 

Number  of 
days 

c 

M 
O 

O 

4^ 

s 

GO 

c 

0i 

cq 

a 

o 
O 

o 
O 

4^ 
C« 

03 

s 

ffl 

CD 

— 

O 

O 

12 


PRACTICE  5 

Determination  of  Total  Moisture  in  the  Same  Soil  Under  Dif- 
ferent Conditions. 

Collect  samples  of  surface,  subsurface  and  subsoil*  from  the  fol- 
lowing places:  (1)  Sod,  (2)  Tilled  field,  (3)  Forest.  In  collecting  these 
samples  care  should  be  taken  to  secure  them  from  as  small  an  area  as 
possible  so  that  soil  conditions  may  be  uniform.  Expose  the  samples 
as  little  as  possible  to  the  air  while  taking  them.  After  taking  them 
to  the  laboratory,  the  contents  of  the  jars  should  be  thoroughly  mixed 
by  shaking.  The  condition  of  the  weather  at  the  time  the  samples 
are  taken  and  also  the  amount  of  rainfall  within  the  week  previous 
should  be  noted. 

Make  the  determinations  in  duplicate.  Weigh  6  soil  pans  and  use 
100  grams  or  more  of  each  soil.  Weigh  rapidly  to  prevent  loss  by  evap- 
oration. Place  in  an  oven  and  leave  at  least  five  hours.  Cool  to  the 
room  temperature  and  weigh  at  once.  The  loss  of  weight  represents 
the  total  water  content. 

It  would  be  well  for  three  students  to  work  together,  one  taking 
the  surface,  another  the  subsurface,  and  the  third  the  subsoil.  These 
results  may  be  compared. 

Explain  differences  in  moisture  content  of  the  soils. 

PRACTICE  5 


Sod 


Student 


Stratum 


Wt.  of 

moist 

soil 


Wt.  of 
water- 
free-soil 


Loss 

in 
Grams 


Percent 
mois- 
ture 


Surface  .  . . . 
Subsurface  . 
1st  Subsoil. . 
2nd  Subsoil. 


*In  collecting  the  subsoil  for  moisture  determination  it  is  sometimes  well  to  divide  it 
into  two  equal  parts  as  to  depth. 


13 
Tilled  Field 


Surface  .  . . . . 

Subsurface  . . 
1st  Subsoil. . . 

2nd  Subsoil.. 

Forest 


Surface 

1st  Subsoil.. . 

2nd  Subsoil. . 

14 

PRACTICE  6 

Determination  of  the  Variation  in  the  Hygroscopic  Capacity 
of  Soils. 

In  this  exercise  each  student  will  use  air-dried  soils  provided  for 
the  purpose.    These  are  sand,  loam,  silt,  clay  and  peat. 

Determine  the  percent  of  moisture  lost  when  heated  for  5  hours 
at  100°  C.  This  is  the  hygroscopic  moisture.  Express  in  percent  of 
water-free  soil.  Care  must  be  taken  to  weigh  out  all  samples  at  the 
same  time  to  avoid  any  change  in  the  amount  of  moisture  due  to  a 
change  in  relative  humidity. 

Explain  differences  between  clay  and  sand. 

Between  peat  and  sand. 


15 
PRACTICE  6 


Soil 

Sand 

Loam 

Silt 

Clay 

Peat 

Sample 

* 

2 

1 

2 

1 

2 

1 

2 

1 

2 

Weight  of  water-free  soil. 

Percent  of  hygroscopic 

16 

PRACTICE  7 

Determination  of  Flocculating  Action  of  Lime. 

Take  four  bottles  and  in  one  put  200  cc.  of  distilled  water,  as  a 
check,  in  another  200  cc.  of  .1  percent  solution  of  lime,  in  another  200 
cc.  .01  percent  and  in  the  fourth  .001  percent  solution.  Add  to  each, 
three  grams  of  finely  ground  clay  and  shake  for  ten  or  fifteen  minutes. 
After  shaking  take  out  a  drop  from  the  check  and  .1  percent  solution 
and  examine  under  a  microscope  with  a  high  power.  Then  pour  some 
of  the  contents  of  the  bottles  into  tubes  and  whirl  in  the  centrifuge, 
stopping  every  two  or  three  minutes  to  note  the  effect  upon  the  clear- 
ness. Whirl  for  at  least  fifteen  minutes.  After  centrifugation,  pour 
the  contents  of  the  tubes  into  their  respective  bottles,  shake  thor- 
oughly and  set  aside,  observing  them  occasionally  to  determine  the 
time  required  for  complete  sedimentation  in  each  case. 

Make  sketches  of  the  appearance  of  the  check  and  the  0.1  per- 
cent solution  under  the  microscope. 

Which  is  thrown  down  first  by  the  centrifuge?    Why? 

What  practical  application  of  this  principle  in  farm  practice? 


17 
PRACTICE  7 


Time  to  Centrifugate      Time  for  Sedimentation 


0.1  %  solution  . . . 

0.01  %  solution.. 

0.001  %  solution. 

Check 


18 

PKACTICE  8 

Determination  of  the  Effects  of  Lime  on  Plastic  Soils. 

Two  students  may  work  together  in  this  experiment. 

Weigh  out  6,300-gram  samples  of  the  clay  soil  using  them  as  follows: 
To  sample 

No.  1,  check,  add  no  lime. 

No.  2  add  .5  gr.  of  air  slacked  lime. 

No.  3  add  1.  gr.  of  air  slacked  lime. 

No.  4  add  5.  gr.  of  air  slacked  lime. 

No.  5  add  10  gr.  of  air  slacked  lime. 

No.  6  add  10  gr.  sand. 

Mix  each  sample  thoroughly  in  a  soil  pan  with  the  lime  and  add 
just  enough  water  to  make  plastic. 

Fill  the  semicircular  moulds,  first  placing  a  damp  thin  cloth  in  it 
to  facilitate  the  removal  of  the  clay.  Make  duplicates  of  each  number, 
being  careful  to  compress  each  to  the  same  degree.  Place  on  a  cloth 
in  a  soil  pan  and  dry  in  an  oven  for  5  hours  at  100°  C. 

Test  the  strength  of  each  brick  by  supporting  the  ends  so  as  to 
allow  just  3  inches  between  points  of  support.  Hang  weight  pan  in 
middle  of  brick  and  determine  the  weight  necessary  to  break  each. 

Explain  the  effect  of  lime. 

Why  does  the  sand  not  have  as  much  effect  as  the  lime  on  the 
breaking  strength? 


19 
PRACTICE  8 


1st  Trial  2nd  Trial  Average 


Check.— No.  lime 
0.5  grams  of  lime  . 
1.  gram  of  lime  . . 
5.  grams  of  lime  . 
10.  grams  of  lime 
10.  grams  of  sand . 


20 

PRACTICE  9 

Determination  of  the  Volume  Weight  and  Apparent  Specific 
Gravity  of  Soils. 

The  volume  weight  of  a  soil  is  the  weight  of  a  certain  unit  of 
volume  and  the  cubic  centimeter  is  taken  as  this  unit.  In  determin- 
ing the  apparent  specific  gravity,  the  pore  space  is  not  taken  into  ac- 
count. This  gives  a  result  much  less,  numerically,  than  the  real  spe- 
cific gravity. 

Find  the  volume  weight  and  apparent  specific  gravity  of  sand,  loam, 
silt,  clay  and  peat. 

Weigh  an  empty  and  thoroughly  cleaned  soil  tube.*  Fill  the 
tube  with  one  of  the  soils  to  be  tested  by  simply  pouring  the  soil  in 
loosely  till  it  reaches  the  crease  near  the  top,  being  careful  not  to  com- 
pact the  soil  by  jarring  or  jolting.  Weigh,  empty  and  then  fill  again 
with  the  same  soil  in  the  same  way,  using  the  average  of  the  two 
weights  of  soil  from  which  to  determine  the  volume  weight  and  ap- 
parent specific  gravity.  Treat  each  soil  in  the  same  way.  Determine 
the  amount  of  water-free  soil  in  each  case  by  using  the  percent  of  hy- 
groscopic moisture  found  in  Practice  6.  Find  volume  of  soil  tube  by 
filling  with  water  to  the  crease  and  weighing.  The  weight  in  grams 
will  give  the  volume  in  cubic  centimeters  since  one  cc.  of  water 
weighs  approximately  one  gram.  The  weight  of  the  soil  divided  by 
the  volume  of  the  tube  will  give  the  weight  of  one  cubic  centimeter 
of  soil  or  the  volume  weight  of  soil.  Numerically,  this  is  the  appar- 
ent specific  gravity. 

Volume  weight  of  soil  ~       ._    _,  .  ~   ., 

—  Apparent  Specific  Gravity  of  Soil- 

Repeat  the  above  process  with  each  soil  but  use  the  compacting 
machine  in  filling  the  tubes,  allowing  the  weight  to  fall  three  times 
from  the  12-inch  mark  upon  each  measure  of  soil. 

The  volume  weight  and  apparent  specific  gravity  of  soils  varies 
with  the  amount  of  compaction.  A  freshly  plowed  field  is  much 
lighter  per  cubic  foot  than  one  compacted  by  rains,  tramping  or  by 
means  of  the  roller. 

Why  is  the  apparent  specific  gravity  of  sand  higher  than  that  of 
loam? 

Why  is  the  apparent  specific  gravity  of  peat  so  low? 

Sand  has  less  pore  space  than  clay. 

How  will  this  affect  the  apparent  specific  gravity? 

What  would  be  the  weight  of  a  cubic  foot  of  each  kind  of  soil  both 
compact  and  loose? 


A  galvanized  iron  tube  two  inches  inside  diameter  and  12  inches  long,  closed  at  one 
A  crease  one  inch  from  the  top  indicates  the  height  to  which  ii  may  lie  tilled- 


21 
PRACTICE 


Soils 

Sand 

Loam 

Silt 

Clay 

Peat 

Cora  pact  ion 

L* 

C 

L 

C 

L 

C 

L 

C    1  L      C 

Weight  of  tube 

Weight  of  tube]  1st  trial. 

+  air-dry  I 

soil J  2nd  trial 

Av.  of  trials 

Percent  of  hygroscopic 

moisture 

No.  of  cc.  of  water  to  fill 
tube 

Apparent  specific  gravity. 

• 

*L  =  loose,  C  =  compact. 


PEACTICE  10 

Determination  of  the  Apparent  Specific  Gravity  of  Surface 
Soil  Under  Field  Conditions. 

Take  a  tube*  provided  for  the  purpose  and  force  it  into  the  ground 
to  the  depth  of  six  inches.  Bemove  soil  to  a  weighed  pan  and  dry  in 
the  oven  at  100°  C.  for  at  least  ten  hours.  Find  volume  of  the  soil 
taken  and  divide  the  weight  of  the  water-free  soil  by  this.  The  re- 
sult will  be  the  apparent  specific  gravity. 

The  apparent  specific  gravity  of  soils  in  the  field  may  be  taken  as 
an  approximate  indication  of  the  tilth,  since  the  better  the  tilth  the 
less  the  apparent  specific  gravity  for  the  same  kind  of  soil.  This  is 
due  to  the  fact  that  soils  in  good  tilth  are  looser  on  account  of  the 
presence  of  a  larger  percent  of  organic  matter  and  better  granulation. 
The  apparent  specific  gravity  of  a  continuously  cropped  soil  is  higher 
than  one  having  proper  rotations.    Why? 

What  would  be  the  weight  of  a  cubic  foot  of  soil  under  the  above 
conditions? 


♦An  iron  or  brass  tube  three  inches  in  diameter  with  a  cutting:  edge.    Very  heavy 
galvanized  iron  will  do. 


23 
PRACTICE  10 


Sample  1  Sample  2 


Weight  of  pan 

Weight  of  pan  +  soil 

Weight  of  soil 

Weight  of  water 

Weight  of  water-free  soil. . 

Volume  of  tube  in  cc 

Apparent  specific  gravity. . 
Weight  of  a  cu.  ft.  of  soil, 


24 

PRACTICE  11 

Determination  of  Real  Specific  Gravity  of  Soils.    Picnometer 
Method. 

Use  sand,  loam,  silt,  clay  and  peat. 

Fill  a  picnometer  to  the  end  of  the  capillary  tube  with  distilled 
water  whose  temperature  is  known.  Wipe  dry  and  weigh.  Pour  out 
about  half  of  the  water  and  add  about  ten  grams  of  soil  (about  half 
as  much  peat)  that  has  been  carefully  weighed.  It  is  a  good  plan  to 
weigh  the  flask  just  before  the  soil  is  added  and  again  just  after,  the 
difference  being  the  weight  of  the  soil.  In  this  case  the  soil  need  not 
be  previously  weighed. 

Boil  gently  for  a  few  minutes  in  the  water  bath,  sand  bath  or  on 
an  asbestos  mat  to  drive  out  the  air  from  the  soil.  Refill  with  dis- 
tilled water,  bring  to  the  same  temperature  as  before  and  weigh. 
Determine  the  amount  of  water-free  soil,  using  the  percent  of  hygro- 
scopic moisture  found  in  Practice  6.  The  weight  of  the  flask  of  water 
plus  the  weight  of  the  soil,  minus  the  weight  of  the  flask  containing 
the  soil  gives  the  weight  of  water  displaced  by  the  soil.  Calculate 
the  specific  gravity  and  tabulate  results. 

Compare  the  real  specific  gravity  with  the  apparent  specific  gravity. 

Why  is  the  real  specific  gravity  higher? 


25 
PRACTICE  11 


Soils 

Sand 

Loam 

Silt 

Clay 

Peat 

Samples 

1 

2 

1 

2 

1 

2 

1 

2 

1 

2 

Weight  of  picnometer 

filled  with  water  -f 
wt.  of  water-free  soil 

Weight  of  picnometer 

containing  soil 

Weight  of  water  displaced 
Weight  of  water-free  soil 

26 

PRACTICE  12 

Determination  of  Porosity. 

first  method. 

"Weigh  the  Nessler's  jar  or  graduated  cylinder. 

Use  sand,  loam,  silt,  clay  and  peat. 

Fill  to  the  50  or  100  cc.  mark  with  soil  not  compacted  and  weigh. 
Compute  the  amount  of  water-free  soil  in  this,  using  the  percent  of 
hygroscopic  moisture  determined  in  Practice  6. 

(Volume  of  soil  x  real  specific  gravity)-Wt.  of  water-free  soil  =  nt  Qf  space 

Volume  of  soil  x  real  specific  gravity 

What  effect  does  size  of  particles  have  on  total  amount  of  pore 
space? 

Does  the  amount  of  pore  space  increase  or  decrease  with  the 
amount  of  organic  matter? 

Which  of  the  soils  have  the  largest  pores?  Does  this  mean  the 
greatest  amount  of  pore  space? 


27 
PRACTICE  12 


Soil 

Sand 

Loam 

Silt 

Clay 

Peat 

Av.  of  two  trials 

Percent    of    hygroscopic 

Percent  of  pore  space 

28 
PRACTICE  13 

Determination  of  Porosity, 
second  method. 

Find  what  percent  the  apparent  specific  gravity  is  of  the  real 
specific  gravity  and  subtract  this  from  100  percent.  The  remainder 
expresses  the  percent  of  pore  space  in  the  soil. 

Use  the  results  in  Practice  9  and  11,  and  determine  the  pore  space 
for  loose  and  compact  soils  and  express  the  results  In  tabular  form. 

The  porosity  of  soils  varies  as  the  apparent  specific  gravity. 

Why? 


29 
PRACTICE  13 


Soil 

Sand 

Loam 

Silt 

Clay 

Peat 

Compaction 

L* 

C 

L 

C 

L 

C 

L 

C 

L 

C 

' 

*L^=loose.    C=compact. 


30 

PRACTICE   14 

Determination  of  Loss  on  Ignition. 

The  loss  that  a  soil  suffers  when  it  is  ignited  is  often  taken  as  a 
measure  of  the  organic  matter,  but  it  can  only  be  a  very  rough  ap- 
proximation at  best  for  most  soils.  For  some  subsurface  and  nearly 
all  subsoils,  it  gives  little  or  no  idea  of  the  amount  of  organic  matter. 
By  igniting,  the  organic  matter,  volatile  salts  and  water  of  hydration 
will  be  driven  off.  In  heavy  clay  soils  and  all  fine  grained  ones,  this 
latter  forms  a  very  large  part  of  the  loss.  Subsoils  with  little  or  no 
organic  matter  may  lose  as  much  as  surface  soils,  due  to  the  larger 
amount  of  clay  and  consequently  a  larger  amount  of  water  of  hydra- 
tion which  is  driven  off  by  the  heat.  The  more  organic  matter  pres- 
ent in  a  soil,  the  nearer  the  loss  on  ignition  will  correspond  to  the 
real  amount  so  that  for  peat  soils,  ignition  may  give  a  close  approxi- 
mation to  the  amount  of  organic  matter  present. 

Weigh  out  5  grams  of  water-free  soil  or  air-dry  soil  calculated  to  a 
water-free  basis  and  ignite  in  a  small  crucible  to  low  red  heat  for  15 
to  20  minutes.  Cool  in  a  desiccator  and  weigh.  Determine  loss  for 
silt,  loam,  clay  and  peat. 

Of  which  of  the  soils  loses  most?    "Why? 

How  do  coarse  and  fine  grained  soils  compare  in  loss? 


31 
PRACTICE  14 


Soils 

Loam 

Silt 

Clay 

Peat 

Sample 

1 

2 

1 

2 

1 

2 

1 

2 

Percent  of  hygroscopic  moisture. . . 

32 

PRACTICE  15 

Determination  of  Humus  in  Soils. 

Weigh  out  five  or  ten  grams  of  water-free  soil,  the  amount  taken 
depending  upon  the  amount  of  humus  in  the  soil.  Plase  in  filter  and 
leach  out  the  lime  and  magnesia  with  dilute  hydrochloric  acid.* 
When  the  lime  is  all  leached  out,  as  shown  by  testing  the  filtrate  with 
ammonia  and  ammonium  oxalate,  wash  out  the  hydrochloric  acid  with 
distilled  water.  Dry  the  soil  and  filter  paper  in  an  oven  at  100°  C. 
and  put  in  a  wide-mouthed  bottle,  carefully  measure  and  add  150  cc. 
to  300  cc.  of  dilute  ammonia,  the  amount  depending  upon  the  richness 
of  the  soil  in  humus.  Shake  for  about  three  hours.  Filter.  Evapor- 
ate 50 cc.  or  100  cc.  of  filtrate  to  dryness.  Dry  at  100°  C,  weigh,  ignite 
and  weigh  again.  The  loss  in  weight  is  the  humus.  Calculate  from 
the  part  evaporated  the  total  amount  of  humus  and  express  in  percent 
of  the  water-free  soil. 

Of  what  benefit  is  a  large  amount  of  humus? 

If  an  acre  seven  inches  of  soil  weighs  2,000,000  pounds,  how  many 
tons  of  humus  per  acre  in  the  soil  with  which  you  are  working? 


•For  the  dilute  dydrochloric  acid  use  25  oc  HC1  sp.  grr.   1.19  with  808  cc  of  distilled 
water.     For  the  ammonia  178  cc  saturated  ammonia  with  422  00  of  distilled  water 


33 
PRACTICE  15 


Soils 

Loam 

Silt 

Clay 

Sample 

1 

2 

1 

2 

1 

2 

Weight   of  crucible   +    air-drj 



Weight  of  water- free  soil . 



Weight  after  ignition        



Loss  of  weight 

Percent  of  humus 

Average 

34 
PRACTICE  16 

Determination  of  Conductivity  of  Soils 


Use  sand,  loam,  silt,  clay,  and  peat. 

In  one  end  of  tray*  place  the  copper  vessel  for  the  water  and  put 
asbestos  plates  on  all  sides  except  the  one  adjacent  to  the  soil.  Fill 
the  tray  with  the  soil  to  be  tested.  Place  thermometers  at  a  depth 
of  2i  inches  and  1,  2,  3,  4,  5  and  6  inches  from  the  vessel  with  the  water 
and  apply  heat  to  the  water  through  the  opening  in  the  bottom  of 
the  tray.  Read  thermometers  about  every  five  or  ten  minutes  for 
about  one  hour.    Tabulate  results. 

Students  should  work  in  sets  of  five,  each  student  testing  one 
soil  and  giving  data  to  other  four  for  comparison.  Is  there  any  rela- 
tion between  porosity  and  conductivity? 


*The  tray  is  made  of  galvanized  iron  18  inches  long  by  5  inches  wide  and  5  inches 
deep.  At  one  end  of  the  bottom  is  a  circular  opening  2  inches  in  diameter  through 
which  heat  is  applied  to  the  copper  vessel  containing  water.  This  is  4"  X  4"  and  five 
inches  deep  with  a  lid  with  two  holes,  one  for  a  thermometer  and  one  for  the  escape  of 
steam. 

PRACTICE  16 


Sand 

Loam 

Time 

Temperature  at 
1" 

2" 

3" 

4" 

5" 

6" 
From  source  of  heat 

35 


Silt 

Clay 

Time 

Temperature  at 
1" 



2" 

... 

3" 

4" 

5 

6" 
From  source  of  heat 

Peat 

Time 

Temperature  at 
1" 

2" 

3" 

4" 

5" 

6" 
From  source  of  heat 

36 

PRACTICE  17 

Power  of  Loose  Soils  to  Retain  Water. 

Fill  tubes*  with  sand,  loam,  silt,  clay  and  peat  soils.  (Fill  tubes 
about  two-thirds  full  of  peat.) 

Place  disks  of  damp  cheese-cloth  in  the  bottom  of  the  tubes  and 
then  weigh  them.  Fill  the  tubes  up  to  the  crease  (except  peat)  one 
inch  from  the  top  by  pouring  the  soil  in  gently  through  a  funnel  as 
the  tube  is  held  vertically,  being  careful  not  to  compact  the  soil  by 
jarring.  Weigh  the  filled  tubes  and  place  in  an  empty  galvanized  iron 
box.  Pour  water  in  the  box  till  it  is  on  the  same  level  with  the  soil 
in  the  tubes,  thus  allowing  the  water  to  pass  up  through  the  soils. 

Note  time  required  for  soils  to  become  moist  on  top.  When  the  soils 
have  become  thoroughly  saturated,  remove  the  tubes  and  place  them 
in  a  pan  to  drain.  Cover  to  prevent  evaporation  and  weigh  when 
drainage  ceases. 

Determine  the  amount  of  water-free  soil  by  using  the  percent  of 
hygroscopic  moisture  found  in  Practice  6. 

Measure  depth  of  the  settled  soils. 

Calculate  the  percent  of  waterretained,  the  weight  per  cubic  foot 
of  soil  that  this  represents  using  the  apparent  specific  gravity  found 
in  Practice  9,  and  the  acre  inches  of  water. 

Land  recently  plowed  6  inches  deep  will  absorb  how  many  inches 
of  rainfall  without  any  run-off? 

Is  there  any  advantage  in  deep  plowing  on  rolling  or  hilly  land? 

What  is  a  saturated  soil? 

Why  do  they  plow  deep  in  semi-arid  regions? 


♦Galvanized  iron  or  copper  tubes  two  inches  inside  diameter  and  twelve  inohes  long 
with  a  crease  one  inch  from  the  top.  The  bottom  is  perforated  with  numerous  small 
holes  and  is  about  one-half  inch  from  lower  end  of  tube.  There  are  two  or  three  holes  in 
main  tube  below  this  for  water  to  enter. 


37 
PRACTICE  17 


Soil 


Sand  Loam    Silt    Clay    Peat 


Weight  of  tube 

Weight  of  tube  +  air  dry  soil . . . 

Weight  of  air-dry  soil 

Percent  of  hygroscopic  moisture . 

Weight  of  water-free  soil 

Time  to  become  moist 

Depth  of  dry  soil 

Depth  of  wet  soil 

Weight  of  water  retained 

Percent  of  water  retained 

Apparent  specific  gravity 

Weight  of  cubic  foot  of  soil 

Pounds  of  water  per  cubic  foot. . 
Acre  inches  of  water 


PRACTICE    18 

Power  of  Compact  Soils  to  Retain  Water 

Use  same  tubes  and  soils  as  in  Practice  17  and  run  at,  the  same 
time  if  possible.  Prepare  the  tubes  in  the  same  way  but  compact  by 
letting  the  weight  drop  three  times  from  the  12  inch  mark  upon  each 
measure  of  soil.  Fill  to  the  crease  except  peat  and  proceed  as  in 
Pr&cticG  17. 

Calculate  the  percent  of  water  retained,  the  weight  of  water  per 
cubic  foot  of  soil  using  the  apparent  specific  gravity  found  in  Practice 
9,  and  the  acre  inches  of  water  for  each  soil. 

Which  soil  becomes  wet  on  top  first?  Why?  How  does  this  cor- 
respond with  total  pore  space?  Which  soil  is  drained  first?  Why? 
How  does  this  correspond  with  total  pore  space? 

How  does  rolling  effect  the  water-holding  capacity  of  a  soil? 


39 
PRACTICE  18 


Soils 


Sand  Loam 


Silt 


Clay    Peat 


Weight  of  tube 

Weight  of  tube  +  air-dry  soil 

Weight  of  air-dry  soil 

Percent  of  hygroscopic  moisture . 

Weight  of  water-free  soil 

Time  to  become  moist 

Depth  of  dry  soil  

Depth  of  wet  soil 

Weight  of  water  retained 

Percent  of  water  retained 

Apparent  specific  gravity 

Weight  of  cubic  foot  of  soil 

Pounds  of  water  per  cubic  foot.. 
Acre  inches  of  water 


40 

PRACTICE  19 

Effect  of  Organic  Matter  on  Retention  of  Water 

Use  same  tubes  as  in  preceding  practices  but  compact  in  one, 
sand,  and  in  the  others  sand  and  peat  in  the  following  proportions: 
95  grams  of  sand  and  5  grams  of  peat  thoroughly  mixed,  90  grams  of 
sand  and  10  grams  of  peat,  80  grams  of  sand  and  20  grams  of  peat  and 
60  grams  of  sand  and  40  grams  of  peat. 

Treat  as  in  the  preceding  and  determine  the  grams  of  water  re- 
tained, also  the  percent  of  water  retained  based  upon  the  total 
amount  of  sand  and  peat  used  in  each  tube. 

How  many  grams  of  water  did  the  5  grams  of  organic  matter  re- 
tain?   The  10  grams?    The  20  grams?    The  40  grams? 


41 
PRACTICE  19 


Soils 


Prac- 
tice 18 
Sand 


Sand 

—  % 
Peat 


Sand 

% 

Peat 


Sand 
-% 
Peat 


Sand 
-% 
Peat 


Weight  of  tube 

Weight  of  tube  +  air-dry 
soil 


Weight  of  air-dry  soil 

Percent     of     hygroscopic 
moisture 


Weight  of  water-free  soil.. 

Time  to  become  moist 

Depth  of  dry  soil 

Depth  of  wet  soil 

Weight  of  water  retained . 
Percent  of  water  retained. 
Apparent  specific  gravity. 


Weight  of  cubic  foot  of  soil . 

Pounds  of  water  per  cubic 
foot 


Acre  inches  of  water. 


Grams  of  water  retained  by 
one  gram  of  peat 


42 

PRACTICE  20 

Determination  of  the  Rate  of  Percolation  of  Air  Through 
Soils 

This  experiment  requires  the  utmost  care  in  order  to  obtain 
satisfactory  results.  Use  the  same  aspirator*  for  all  of  the  soils. 
Be  sure  that  all  connections  are  air  tight.    Use  pressure  tubing. 

Fill  the  tubes  very  carefully  without  compacting,  holding  them 
vertically  while  filling.  Attach  the  tubes  successively  to  the  aspirator 
after  the  can  has  been  lowered  in  the  water  to  the  zero  mark.  Allow 
at  least  4  litres  of  air  to  pass  through  each  soil  and  express  results  in 
time  required  for  10  litres  of  air  to  pass  through.  Empty  tubes  and 
refill  and  run  again  as  a  check. 

Use  sand,  loam  and  clay,  compacting  by  letting  the  weight  fall 
three  times  from  the  foot  mark  upon  each  measure  of  soil.  Tabulate 
your  results  for  both  loose  and  compact. 

What  bearing  has  this  experiment  upon  aeration? 

What  effect  does  organic  matter  have  on  aeration? 

What  effect  will  moisture  in  the  soil  have  upon  aeration? 

Try  it  by  wetting  the  tube  of  sand  and  then  drawing  air  through 
it. 

One  student  may  run  sand  with  10  grams  of  organic  matter  (peat) 
and  another  clay  with  the  same  proportion  and  compare  with  the 
results  from  the  stock  sand  and  clay.  Give  to  the  class  for  compari- 
son. 


♦The  aspirator  B  is  made  of  galvanized  iron,  8  inches  in  diameter  and  about  18  inches 
long  fitted  with  a  stopcock  to  which  the  rubber  tube  is  attached  that  runs  to  tube  D  in 
which  the  soil  is  placed.  The  aspirator  fits  loosely  in  a  can  C  filled  with  water.  Tube  D 
is  made  of  galvanized  iron  and  is  2  inches  in  diameter  and  18  inches  lonif  with  a  tube  for 
attaching  to  the  rubber  tube  from  the  aspirator.  A  is  the  weight  and  should  be  at  least 
twice  as  heavy  as  can  B. 


43 
PRACTICE  20 


Sand 

Loam 

Clay 

Loose 

Com- 
pact 

Loose 

Com- 
pact 

Loose 

Com- 
pact 

1 

14 


PRACTICE  21 

Determination  of  the  Rate  of  Percolation  of  Water 
Through  Soils. 

Fill  the  tubes*  provided  for  the  purpose  with  the  soils,  without 
compacting,  to  within  a  half  inch  of  the  overflow  tube  and  place  a 
layer  of  coarse  sand  one  half  inch  deep  on  top  to  prevent  the  dis- 
turbance of  the  soil  by  the  flowing  water. 

Connect  the  tubes  as  in  the  figure  by  means  of  short  rubber 
tubes.  Attach  a  to  the  water  supply  and  b  should  lead  to  the  waste 
pipe  or  sink  for  taking  off  the  overflow.  Allow  the  water  to  flow 
over  the  surface  of  the  soil  just  fast  enough  to  keep  it  constantly 
flooded.  Place  flasks  under  the  tubes  c  to  catch  any  drainage  water. 
Note  the  time  when  water  is  turned  on  and  also  when  percolation 
begins.  When  the  flow  becomes  constant,  the  quantity  of  water 
draining  from  the  soil  in  30  minutes  is  determined. 

Use  the  same  soils  in  the  same  way  but  compact  them  in  the 
usual  manner. 

What  application  of  this  experiment  do  we  see  in  farm  practice? 

From  this  experiment,  would  it  be  advisable  to  plow  deep? 

Would  there  be  any  advantage  in  fall  plowing? 

What  objection  to  a  sandy  soil  does  this  experiment  show? 


fr\ 


X 


=   ^ 


*The  tubes  are  of  galvanized  iron  2  inches  inside  diameter.  The  overflow  tubes, 
about  %  inch  in  diameter,  are  1  inch  from  the  top  and  the  M  inch  bent  drainage  tube  is 
Vi  inch  from  the  bottom. 


45 
PRACTICE  21 


Sand 

Loam 

Silt 

Loose 

Com- 
pact 

Loose 

Com- 
pact 

Loose 

Com- 
pact 

Time  when  percola- 
tion begins 

Amount  of  water 
percolating 
in  30  min 

46 

PRACTICE  22 

Testing  the  Tenacity  of  Moist  Soils. 


Use  clay,  silt  and  loam. 

Weigh  out  about  200  grams  of  each  soil  to  be  tested.  Pour  the 
soil  in  a  pan  and  mix  with  it  by  hand  enough  water  to  bring  it  to 
maximum  adhesiveness  as  near  as  you  are  able  to  judge. 

Note  amount  of  water  used. 

Now  holding  the  cages  firmly  together,  pack  the  mud  into  them 
and  scrape  the  top  off  level.  Attach  the  weight  pan  and  carefully 
pour  sand  or  fine  shot  into  it  until  the  soil  column  breaks.  Weigh  pan 
and  sand.  Put  the  movable  cage  in  place  but  not  having  the  soil 
surface  in  contact,  and  determine  the  weight  necessary  to  overcome 
friction. 

Subtract  this  from  the  previous  weight.  The  result  represents 
the  tenacity  of  a  column  of  moistsoil  one  square  inch  in  cross  section. 

With  the  same  roll  of  mud,  make  three  tests,  using  different 
amounts  of  water,  noting  the  amount  added  for  each  soil  each   time. 

How  does  fineness  of  grain  effect  tenacity? 

What  effect  would  undecomposed  organic  matter  have  on  tena- 
city? 

What  term  is  applied  to  very  tenacious  soils? 

What  differences  in  the  working  of  these  soils? 


47 
PRACTICE  22 


Soils 

Silt 

Loam 

Clay 

Weight  to  overcome  friction. . 

Breaking  force     I 

2nd  trial 

48 

PRACTICE  23 

Eefbct  of  Organic  Matter  on  Kise  of  Water. 

Class  exercise  in  which  each  member  of  the  class  is  to  take  daily 
observations  on  the  height  of  the  water  in  the  tubes  and  note  effect 
of  organic  matter  on  rise  of  water. 

After  tying  a  cloth  firmly  over  the  ends  of  two  glass  two-inch  tubes, 
18  inches  long,  fill  them  to  the  height  of  one  foot  with  soil  compacted  by 
letting  the  tube  drop  four  times  on  a  book  for  a  distance  of  six  inches 
for  every  six  inches  of  soil  put  in  the  tube. 

In  one  tube  put  about  an  inch  of  cut  straw  or  sawdust,  in  the 
other  about  a  half  inch  of  well  decomposed  manure  or  peat.  Fill  the 
tubes  with  soil.  Place  the  ends  of  the  tubes  in  a  tray  and  note  the 
effect  of  the  organic  matter. 

What  is  the  effect  of  plowing  under  poorly  rotted  manure  in  the 
spring? 

What  advantage  in  this  respect  in  fall  plowing? 


49 

PRACTICE  24 
A  Study  of  tiie  Capillary  Power  of  Soils. 
The  capillary  power  of  soils  is  influenced  by  several  factors,  the 
most  important  of  these  being  the  physical  composition,  texture  and 
compactness  of  the  soil.    In  field  soils  all  of  these  are  changed  by  con- 
tinuous cropping  and  capillary  action  is  therefore  altered.    Of  these 
factors,  physical  composition   is   most   important. 
The  soils  selected  are  as  follows: 

1.  Peat. 

2.  Sod,  preferably  an  old  blue  grass  pasture. 

3.  Heavily  cropped  soil  as  near  (2)  as  possible  so  that  the  type  of 
soil  will  be  the  same. 

4.  Clay. 

5.  Silt. 

6.  Loam. 

7.  Loess. 

8.  Sand  that  will  pass  a  100  mesh  sieve  but  not  a  120. 

9.  Sand  that  will  pass  an  80  mesh  sieve  but  not  a  100. 

10.  Sand  that  will  pass  a  60  mesh  sieve  but  not  an  80. 

11.  Sand  that  will  pass  a  48  mesh  sieve  but  not  a    60. 

12.  Sand  that  will  pass  a  20  mesh  sieve  but  not  a    40. 

13.  Sand  and  clay  equal  parts  by  weight. 

14.  Loess  and  clay  equal  parts  by  weight. 

15.  Loess  and  sand  equal  parts  by  weight. 

16.  Loess  with  10  per  cent  of  well  ground  peat. 

17.  Sand  with  10  per  cent  of  well  ground  peat. 

18.  Clay  with  10  per  cent  of  well  ground  peat. 

19.  Silt  and    5  per  cent  peat. 

20.  Silt  and  10  per  cent  peat. 

21.  Silt  and  15  per  cent  peat. 

22.  Silt  and  20  per  cent  peat. 

23.  Silt  and  35  per  cent  peat. 

24.  Silt  and  50  per  cent  peat. 

One  end  of  the  large  glasstubes  is  closed  by  means  of  a  piece  of 
muslin  firmly  tied  on.  These  tubes  are  then  filled  with  the  finely 
pulverized  and  sifted  air-dried  soils.  Great  care  must  be  exercised 
in  filling  these  tubes  so  as  not  to  separate  the  coarse  and 
fine  particles.  This  may  best  be  accomplished  by  holding  the  tube 
vertically  during  the  process  of  Ailing.  When  the  tubes  are  filled, 
the  soil  is  compacted  slightly  by  letting  each  tube  drop  4  times,  a 
distance  of  4  inches  upon  a  book.  The  tubes  are  now  placed  in  the 
supporting  frames  in  such  a  manner  that  the  ends  shall  dip  one  half 
inch  beneath  the  surface  of  the  water  contained  in  the  tray.  The 
water  should  be  turned  in  all  trays  at  the  same  time.  The  exper- 
iment is  now  ready  for  observation  and  the  data  to  be  obtained  at 
each  reading  is  the  total  hight  to  which  the  water  has  risen.  The 
readings  are  to  be  taken  as  nearly  as  possible  at  the  intervals  stated 
below  and  tabulated. 


50 

Observe  night  after  $  hour,  1  hour.  2  hours,  3  hours,  6  hours,  9 
hours,  12  hours,  24  hours,  36  hours,  48  hours,  3,  4,  5,  6,  7  and  8  days. 

Make  a  close  comparison  of  the  different  tubes. 

Which  shows  the  most  rapid  rise,  8  or  11?  6  or  7?  Why? 

Plot  the  bights  of  the  water  of  the  different  tubes  at  different 
times? 

Why  does  loess  show  a  greater  and  more  rapid  rise  than  clay? 

At  the  end  of  one  hour  which  shows  the  greater  rise,  clay  or  20 
sand?    Which  at  the  end  of  a  week?    Why? 

What  effect  does  organic  matter  have  as  shown  in  2  and  3,  4  and 
18,  7  and  16  and  12  and  17  and  19  to  24? 

What  effect  does  size  of  particles  have  on  rapidity  of  capillary 
movement  not  taking  bight  into  account? 


51 


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52 


PRACTICE  2j 

Effect  of  Soil  Mulches  on  Evaporation  of  Water  from  Soils. 

Fill  all  of  the  tubes*  with  the  same  kind  of  soil  compacting  each 
three  inches  of  soil  added.  The  enlarged  bases  of  the  tube  are  then 
partially  filled  with  water  and  the  tubes  are  left 
till  the  surface  soil  becomes  moist.  The  tubes  are 
then  ready  for  use.  The  water  must  be  replaced 
from  day  to  day,  as  it  evaporates  from  the  surface 
by  refilling  the  base,  the  exact  amount  of  water 
added  in  each  case  being  noted. 

The  loss  of  water  is  determined  by  the   loss  in 
weight  of  the  tubes.    Weigh  each  day. 
Tube  1.  Check  (no  cultivation). 
Tube  2.  Cultivated  1  inch  deep. 
Tube  3.  Cultivated  2  inches  deep. 
Tube  4.  Cultivated  3  inches  deep. 
Tube  5.  Cultivated  4  inches  deep. 
The  cultivations  should   be  made  every  other 
day  to  the  required  depth. 

Each  tube  has  an  area  of  thirty-six  square 
inches  and  the  results  are  to  be  computed  in  tons  of  water  evapo- 
rated per  acre  per  week. 

It  is  very  necessary  that  the  tubes  all  have  the  same  exposure  to 
heat  and  air  currents. 

Upon  what  principle  does  a  soil  mulch  conserve  moisture? 
What  effect  will  cultivation  have  on  a  very  wet  soil? 
If  the  water  table  were  12  inches  from  the  surface  instead  of  what 
it  is,  what  difference  would  there  be  in  your  results? 

Is  there  any  argument  in  the  experiment  in  favor  of  fall  plowing? 
What  argument  for  cultivating  as  soon  after  a  beating  rain  as 
possible? 


*The  tubes  may  be  made  of  galvanized  iron,  zinc  or  copper.  Each  tube  consists  of 
two  parts,  a  straight  tube  28"  long  and  6%"  in  diameter  for  holding  the  soil  and  an 
enlarged  base  9"  in  diameter  and  3"  high  for  holding  the  water.  The  former  is  olosed 
by  tying  a  piece  of  muslin  over  the  end-  The  opening  of  the  basal  part  Is  olosed  by  a 
flange  about  3"  from  the  end  of  the  large  tube.  The  small  tube  is  for  adding  water  as  it 
evaporates. 


53 
PRACTICE  25 


Soil 

Depth  of  Cultivation 

No 
Culti- 
vation 

linch 
deep 

2  inches 
deep 

3  inches 
deep 

4  inches 
deep 

Total  evaporation  in  grams. 
Tons  per  acre  per  week 

54 

PRACTICE  26 

Effect  of   Artificial   Mulches   upon   Evaporation  of  Water 
from  Soils. 

Fill  tubes  as  in  preceding  exercise  to  within  one  inch  of  top  and 
then  fill  the  remaining  part  with  material  for  mulch.  Proceed  as  in 
Practice  25. 

Tube  1.  Check  (filled  to  top  with  same  kind  of  soil). 

Tube  2.  One  inch  of  sand. 

Tube  3.  One  inch  of  gravel. 

Tube  4.  One  inch  of  peat. 

Tube  5.  One  inch  of  sawdust  or  cut  straw. 

The  area  of  each  tube  is  thirty-six  square  inches. 

Compute  loss  of  water  in  tons  per  acre  per  week  and  tabulate 
results. 

What  will  be  the  effect  of  these  mulches  on  temperature? 

What  is  the  principle  of  the  growing  of  "Straw  potatoes,"  i.  e. 
covered  with  straw  and  not  cultivated? 


Soil 


Mulch 


55 
PRACTICE   26 


No 

mulch 


1  inch 
sand 


1  inch 
gravel 


1  inch 
peat 


1  inch 
saw- 
dust 


Total  evaporation  in  grams. 
Tons  per  acre  per  week 


56 

PRACTICE  27. 

Effect  of  Different  Surfaces  upon  Evaporation. 


Fill  all  tubes  with  the  same  kind  of  soil  to  within  one  inch  of  top 
by  compacting. 

Fill  one  tube  to  the  top  with  the  same  kind  of  soil  and  the  others 
with  the  material  desired. 

No.  1.  Check  (filled  to  top  with  same  kind  of  soil). 

No.  2.  One  inch  of  sand. 

No.  3.  One  inch  of  peat. 

No.  4.  One  inch  of  sawdust  or  cut  straw. 

No.  5.  One  inch  of  gravel. 

No.  6.  Pan  of  same  area  filled  with  water. 

The  area  of  each  tube  is  thirty-six  square  inches. 

Conduct  this  practice  similar  to  preceding,  computing  loss  of 
water  in  tons  per  acre  per  week.    Tabulate  results. 


57 
PRACTICE  27 


Surface 

Soil 

Sand 

Peat 

Saw- 
dust 

Gravel 

Water 

Total  evaporation  in 
grams 

Tons    per    acre    per 
week 

58 


PRACTICE  28 


Use  eye-piece  and  stage  micrometers.  Place  both  micrometers 
in  position  and  determine  the  number  of  divisions  or  spaces  of  the 
eye-piece  micrometer  that  correspond  tol,  .1,  .01  and  .001  millimeters 
of  the  stage  micrometer  for  each  of  the  objectives. 

By  means  of  this  table  and  the  microscope  with  the  eye-piece 
micrometer,  it  may  be  determined  whether  the  separations  are  prop- 
erly made  in  the  following  Practice. 


59 
PRACTICE  28 


Grades 

Diameter  in 
millimeters 

inch 

objective 

inch 

objective 

inch 

objective 

Clay 

.001-less 
.001-  .01 
.01  -  .1 

Silt 

.1    -1.0 

Gravel 

1.0  -more 

60 


PRACTICE  29 
Mechanical  Analysis. 

Four  samples  of  from  five  to  ten  grams  of  the  prepared  soil  are 
weighed  out  and  the  hygroscopic  moisture  determined. 

Two  of  these  are  then  ignited  and  the  percent  of  loss  on  ignition 
is  found  based  upon  the  water-free  soil.  Each  of  the  other  two  sam- 
ples is  placed  in  a  shaker  bottle  and  about  200  cc.  of  distilled  water 
and  from  5  to  10  drops  of  ammonia  are  added.  The  bottles  are  then 
placed  in  the  shaker  and  agitated  till  a  microcopic  examination  of  a 
drop  of  the  contents  shows  that  the  soil  particles  are  completely  sep- 
arated and  no  granules  exist.  When  this  condition  is  reached,  the 
individual  particles  will  appear  clear  or  semi-transparent  in  the  field 
of  the  microscope  while  any  remaining  granules  will  be  dark,  irregular 
and  opaque.  It  may  be  necessary  to  continue  the  shaking  for  twelve 
or  even  twenty-four  hours  tocompletely  disintegrate  the  soil  granules. 
As  the  determination  is  quantitive,  but  a  small  amount  of  the  liquid 
is  taken  from  the  bottle  with  a  small  glass  tube  and  mounted  on  a  slide 
for  examination.  When  the  examination  is  completed,  the  slide  and 
cover  glass  are  carefully  rinsed  with  distilled  water  back  into  the  bot- 
tle to  recover  the  small  portion  of  soil  taken.  Great  care  is  necessary 
throughout  the  analysis  to  prevent  the  loss  of  any  part  of  the  sample, 
and  for  purposes  of  comparison  and  greater  accuracy  in  results,  dupli- 
cate samples  are  used. 


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61 

When  the  microscope  reveals  that  no  compound  granules  remain, 
the  samples  are  ready  for  separation  into  the  different  grades.  Re- 
move stoppers  from  the  shaker  bottles  and  wash  them  off  carefully 
with  distilled  water  so  as  to  save  all  of  the  adhering  particles.  Make 
an  apparatus  similar  to  figure  using  an  inverted  2-hole  rubber  stop- 
per so  large  that  it  will  close  the  mouth  of  the  bottle  without  going 
in.  Place  in  one  hole  a  short  bent  tube  and  in  the  other  a  long  tube 
that  reaches  near  the  bottom  of  the  bottle.  The  lower  end  of  this 
tube  should  bend  suddenly  upon  itself  so  that  the  opening  shall  be 
upward  and  not  downward.  Adjust  this  tube  when  the  apparatus  is 
in  place  on  the  bottle  so  that  the  opening  in  the  long  tube  will  be  H 
inches  from  the  bottom  of  the  bottle.  Make  a  mark  on  the  bottle  3 
inches  from  the  bottom.  Fill  the  bottles  to  this  mark  by  means  of  a 
small  stream  of  water  of  sufficient  force  to  thoroughly  stir  up  the  con- 
tents. 

After  the  liquid  has  stood  long  enough  for  the  fine  sand  to  settle 
below  the  end  of  the  tube  as  shown  by  a  microscopic  examination  of 
a  sample  compared  with  the  sizes  of  the  grades  in  the  preceding  exer- 
cise, the  liquid  is  blown  off  into  a  beaker  provided  for  the  purpose. 
This  operation  of  filling,  settling  and  blowing  off  is  repeated  until 
the  grades  that  settle  are  free  from  silt  and  clay.  The  liquid  blown 
off  contains  silt  and  clay  and  no  effort  is  made  to  separate  them  here. 
For  separating  the  fine  sand,  fill  the  bottles  as  before  and  allow 
to  stand  long  enough  for  the  sand  (.1-1  mm.)  to  settle  below  the  tube 
as  shown  by  the  microscope  and  then  blow  off  the  fine  sand.  Repeat 
until  all  the  fine  sand  is  blown  off.  The  sand  and  gravel  may  be  sep- 
arated by  the  use  of  the  millimeter  sieve. 

If  at  any  time  during  the  analysis,  it  is  found  that  some  of  the 
wrong  grade  is  blown  over,  it  will  be  necessary  to  recover  this.  The 
water  containing  the  silt  and  clay  is  poured  into  a  large  bottle  and 
thoroughly  shaken  when  an  aliquot  part  or  500  cc.  is  taken  and  evap- 
orated to  dryness,  placed  in  a  crucible,  ignited,  weighed  and  the  total 
amount  of  clay  and  silt  determined  and  the  percent  found. 

The  water  containing  the  fine  sand,  sand  and  gravel  is  decanted, 
each  grade  is  put  in  a  weighed  crucible,  dried,  ignited  and  the  percent 
of  each  grade  is  determined. 


62 
PRACTICE  29 


Soils 


Grams 


Percent 


Grams 


Percent 


Wt.  of  crucible 

Wt.  of  cru.+air   dry  soil. 
Wt.  after  drying  in  oven. 

Hygroscopic  moisture 

Wt.  after  ignition 

Loss  on  ignition 

Clay,  less  than  .001 

Silt  .001-.01 

Fine  sand  .01-1 

Sand  .1-1 

Gravel  1-more 


63 

PRACTICE   30 

The  last  two  weeks  of  the  semester  will  be  devoted  to  the  estima- 
tion of  the  constituents  of  a  larger  number  of  soils.  It  is  quite  im- 
portant that  one  should  be  able  to  estimate  approximately  the  amount 
of  gravel,  sand,  silt,  clay  and  organic  matter  in  soils  and  it  is  the  ob- 
ject of  this  exercise  to  enable  the  student  to  do  this.  Each  one  will  be 
given  a  sample  of  soil  to  be  studied  according  to  the  outline  below. 
The  work  is  to  be  done  rapidly  and  the  graduated  cylinder  may  be  used 
as  an  aid  in  estimating  the  amount  of  each  constituent. 

In  using  the  graduated  cylinder,  place  10  cc.  of  soil  in  it  and  almost 
fill  with  water.    Shake  thoroughly  and  allow  it  to  stand  for  one-half 
minute  or  longer.    Note  the  amount  of  sand  in  cubic  centimeters. 
Soil  No. 
Dry 
Color 
Odor 

Pulverulent,  crumbly,  cloddy. 
Moist 
Color 
Odor 

Floury,  mealy  or  gritty 
Friable  or  plastic 
Composition 
Organic  matter  (estimated)  in  percent 
Gravel  (estimated)  in  percent 
Sand  (estimated)  in  percent 
Silt  and  clay  (estimated)  in  percent 
Name  of  soil. 


64 

PRACTICE  31 

Determination  of  the  Effect  of  Cultivation  and  Mulches 
upon  Temperature  and  Moisture. 

A  number  of  students  may  work  at  this  experiment,  each  one  be- 
ing assigned  a  definite  problem. 

Select  a  level  area  of  four  or  five  square  rods  and  remove  any  veg- 
etable matter,  such  as  weeds,  etc.  Break  up  with  plow  or  spade  all 
but  one  square  rod.  Place  a  mulch  of  straw  or  leaves  several  inches 
deep  upon  a  half  square  rod  of  both  the  plowed  and  the  unplowed. 
Roll  a  portion  of  the  plowed  area. 

Determine  temperature  at  one,  two  and  four  inches  in  depth 
on  days  when  the  sun  is  shining.  Read  the  thermometer  every  two 
hours. 

Determine  moisture  to  a  depth  of  forty  inches  once  each  week  for 
at  least  four  weeks. 


14  DAY  USE 

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